This invention is concerned with a blowing process for expanding a molten glass parison to the shape of a mould cavity in which the parison is contained to thereby form the parison into an article of glassware, the method comprising supplying air under pressure to the interior of the parison so that an elevated pressure is created in the parison causing it to expand.
In the manufacture of hollow articles of glassware, a gob of molten glass containing sufficient glass to form one article is formed into a parison. The parison is an intermediate shape between the gob and the finished article and has a hollow interior. Parisons are either created by pressing or by a blowing operation. When the parison is created by pressing, the gob of molten glass is introduced into a "blank" mould in which the gob rests on top of a plunger. The plunger is then moved to press the glass to the shape of the mould and the plunger is withdrawn leaving a cavity in the glass which forms the hollow interior thereof. When the parison is formed by a blowing operation, the gob is introduced into the blank mould on top of a plunger which is then withdrawn leaving a hollow space in the gob into which air is blown to cause the glass to expand to the shape of the mould.
However the parison is formed, it is removed from the blank mould and transferred to a "finish" mould in which it is blown to the shape of the mould cavity by supplying air under pressure to the interior of the parison. The air is supplied by means of a blow head which, in most cases, comprises a tube which enters the neck of the parison and the air is supplied through this tube. It is necessary to extract heat from the interior of the parison during the blowing process so that the glass is set in the shape of the article. The heat is extracted by the air which is blown into the parison which leaves through the neck of the parison and through an exhaust passage in the blow head. Thus, during the blowing process there is a continual flow of air into the parison and out through the neck thereof. The time which is taken in the finish mould is a limiting factor on the speed of production of articles of glassware and this time is limited itself by the necessity to allow sufficient time for the heat extraction.
It is an object of the present invention to provide a blowing process for expanding a molten glass parison in which the heat can be extracted from the interior of the parison more rapidly thereby speeding up the process.